Authentication of email senders via authorizing DNS server

ABSTRACT

A DNS server receives from a receiving email system, a DNS query for an email domain stored at the DNS server, the DNS query including identifying information of a sender of an email. The DNS server extracts the identifying information of the email sender from the DNS query and identifies one of a plurality of delivering organizations from the information. The DNS server determines whether the identified delivering organization is authorized to deliver email on behalf of the email domain. In response to determining that the identified delivering organization is authorized to deliver email on behalf of the email domain, the DNS server generates a target validation record based on the identity of the authorized delivering organization and the email domain, the target validation record including one or more rules indicating to the receiving email system whether the delivering organization is an authorized sender of email for the email domain.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/360,322 filed on Jun. 28, 2021, which is a continuation of U.S.application Ser. No. 17/128,008 (now U.S. Pat. No. 11,057,437), filed onDec. 19, 2020, which is a continuation application of U.S. applicationSer. No. 16/296,121, (now U.S. Pat. No. 10,897,485) filed on Mar. 7,2019, which is continuation of U.S. application Ser. No. 15/663,771 (nowU.S. Pat. No. 10,257,231), filed on Jul. 30, 2017, which is acontinuation U.S. application Ser. No. 15/175,031 (now U.S. Pat. No.9,762,618), filed on Jun. 6, 2016, which is a continuation ofInternational Application No. PCT/US2016/015796, filed on Jan. 29, 2016,which claims the benefit of U.S. Provisional Application No. 62/116,409,filed on Feb. 14, 2015, all of which are hereby incorporated byreference in their entirety for all purposes.

BACKGROUND Field of Art

The disclosure generally relates to the field of electronic messaging,and specifically to centralized validation of email senders via EHLOname and IP address targeting.

Description of Art

In distributed messaging systems like email, the actual originator of amessage may be validated against the message's purported identity inorder to eliminate fraudulent messages. Examples of such fraudulentmessages may include “phishing” emails that purport to be from aparticular sender but in fact have a spoofed sender address and are sentfrom a malicious entity that may wish to perform some fraudulentactivity against the recipient (e.g., steal personal information). Oneapproach to this validation problem is to enable the owner of thesending identity to create a set of rules defining which computers areallowed to relay emails to the recipient's email server. Sender PolicyFramework (SPF) is the standard implementation of this approach foremail. A sending identity publishes these SPF rules via the Domain NameSystem (DNS) such that a receiving mail server may be able to accessthem in order to validate the sender's identity of received messages.

While this approach can be effective, it places substantial burdens onthe receiving system and introduces challenges with the use of validintermediaries (e.g. mailing lists, ‘lifetime’ email accounts). Forexample, a mailing list server may be asked to forward a message from anoriginal sender, however, the mailing list server is not identified bythe original sender as a valid sender. It is simply not feasible forreceiving systems to check more than a few such rules when validating amessage, even though a complete rule set might require hundreds or eventhousands of rules.

SPF also includes tight limits on the number of Domain Name System (DNS)lookups that are allowed, in order to limit the burden on receivingsystems, but this comes at the cost of failing to validate somelegitimate messages. Other techniques, like Sender Rewriting Scheme(SRS), replace the original sender with an intermediate identity thatcan be validated with a more restricted rule set. While this minimizesthe burden on the receiving system, it does not validate the messageagainst the originator's identify.

Hence, what is lacking is an ability to allow the definition ofarbitrarily large and complex rule sets for sender identityverification, without unduly burdening receiving systems, and which iscompatible and interoperable with existing frameworks.

SUMMARY

In some embodiments, systems and methods may comprise reframing theauthentication questions around email from the network or IP level tothe sending organization level, utilizing the ability of the existingSender Policy Framework (SPF) protocol to encode network informationavailable from the SMTP connection into a targeted domain name, andcombining that with a custom DNS system backed by a database that mapsthat network information to a list of known organizations.

In some embodiments, systems and methods allow domain managers to definea set of organizations that are able to send email on their behalfwithout any additional work, such as manual lookup of SPF records forauthorized organizations, modification of DNS TXT records for thedomain, etc. It also allows domain manager to authorize any number ofsending organizations, and frees the domain manager of the need to trackchanges to the SPF configuration for authorized senders.

In some embodiments, systems and methods may comprise a Sender PolicyFramework (SPF) which may be the protocol by which the owners of adomain can define a set of rules (known as directives) in a DNS TXTrecord designating which mail servers can deliver emails originatingfrom that domain. Receiving mail servers evaluate those rules and, basedon the IP address of the delivering server, determine whether themessage in question is allowed to originate from that domain.

In some embodiments, systems and methods may utilize two features ofSPF. First, the ‘include’ mechanism, by which an SPF record canreference a target domain where an additional DNS SPF record is defined,and include the rules defined in this reference record into theevaluated rule set. Second, the macro system by which request-specificvalues such as the IP address and EHLO name associated with the SMTPconnection can be interpolated into the target domain.

In some embodiments, when configuring a domain, an SPF record may beconstructed for the domain that incorporates an ‘include’ directive thatuses SPF macros to encode the name of the domain for which an email isbeing authorized, as well as the EHLO name and/or IP address of the SMTPconnection into a target domain name. The target domain name may beconstructed so as to be in a DNS zone managed by the targeted SPF DNSresolver—the DNS system responsible for mapping network information to alist of known organizations.

In further embodiments, the targeted SPF DNS resolver may be responsiblefor responding to DNS queries to target domains. It may also beresponsible for maintaining an accurate and up-to-date mapping ofnetwork information to known organizations, which may involve combiningpublic information such as domain registration records, public DNSentries, and curated information.

In further embodiments, systems and methods for enhancing sender policyframework (SPF) may advance the art of authenticating email, by reducingthe overall complexity and maintenance burden exposed to a domainmanager and removing existing limitations of the state of the artsystems for providing similar authentication. In addition, the methodsmay not require any changes to the systems receiving email, and may becompatible with the existing and extensive base of installed software.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed embodiments have advantages and features which will bemore readily apparent from the detailed description, the appendedclaims, and the accompanying figures (or drawings). A brief introductionof the figures is below.

FIG. 1 illustrates an example system capable of validating email sendersthrough intermediaries via EHLO name and IP address targeting accordingto an embodiment.

FIG. 2 is an interaction diagram and flow chart illustrating anexemplary process for creation of an email domain validation record foruse with a third party delivering organization according to oneembodiment.

FIG. 3 is an interaction diagram and flow chart illustrating anexemplary process for resolution of an email domain validation recordusing DNS according to one embodiment.

FIG. 4 is a block diagram illustrating components of an example machineable to read instructions from a machine-readable medium and executethem in a processor (or controller).

DETAILED DESCRIPTION

The Figures (FIGS.) and the following description relate to preferredembodiments by way of illustration only. It should be noted that fromthe following discussion, alternative embodiments of the structures andmethods disclosed herein will be readily recognized as viablealternatives that may be employed without departing from the principlesof what is claimed.

Reference will now be made in detail to several embodiments, examples ofwhich are illustrated in the accompanying figures. It is noted thatwherever practicable similar or like reference numbers may be used inthe figures and may indicate similar or like functionality. The figuresdepict embodiments of the disclosed system (or method) for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles described herein.

Configuration Overview

Disclosed by way of example embodiments is a system and process capableof validating email senders through intermediaries via EHLO name and IPaddress targeting. In an embodiment, a DNS server receives from areceiving email system, a DNS query for an email domain stored at theDNS server, the DNS query including identifying information of a senderof an email, and the email identifying itself as being from the emaildomain. The DNS server extracts the identifying information of the emailsender from the DNS query, and identifies one of a plurality ofdelivering organizations from the identifying information. The DNSserver determines whether the identified delivering organization isauthorized to deliver email on behalf of the email domain. In responseto determining that the identified delivering organization is authorizedto deliver email on behalf of the email domain, the DNS server generatesa target validation record based on the identity of the authorizeddelivering organization and the email domain, the target validationrecord including one or more rules indicating to the receiving emailsystem that the delivering organization is an authorized sender of emailfor the email domain, and sends the target validation record to thereceiving email system in response to the DNS query.

In one embodiment, a sending email system is configured to create anemail domain validation record to include in a DNS record of an emaildomain, the email domain validation record to be parsed by a receivingemail system when receiving an email from the target domain, andindicating to the receiving email system whether the sender of an emailis an authorized sender for the email domain. To create the email domainvalidation record, the sending email system composes the email domainvalidation record to include a target domain, the target domain being adomain distinct from the email domain, causing the receiving emailsystem, when parsing the email domain validation record, to submit asecond request for a validation record to the target domain. The sendingemail system also composes the email domain validation record to includeone or more macro statements specifying identifying information, themacro statements causing the receiving email system, when parsing theemail domain validation record, to include identifying information ofthe sender of the email in the second request. The sending email systemis configured to publish this created email domain validation record asa DNS record of the email domain.

Introduction

Sender Policy Framework (SPF) is a powerful tool for authenticatingemail, but as used today it has some substantial limitations that makeit difficult to configure, and impose significant limitations on thenumber of services that can, in practice, be authenticated to deliveremail for a given email domain. In some embodiments, systems and methodsmay provide a method by which email domain owners can support a)configuration of SPF authentication of their email domains in terms ofservices, not networking primitives and b) configuration of an unlimitednumber of these services.

Example Key Delegation System

FIG. 1 illustrates an example system 100 capable of validating emailsenders through intermediaries via EHLO name and IP address targetingaccording to an embodiment. The system 100 includes a network 150, oneor more client devices 160, authorizing DNS server 130, domain owner DNSserver 140, a domain owner system 110, a delivering email system 115,and a receiving email system 120. Although the illustrated system 100includes the elements shown in FIG. 1, in other embodiments the system100 may include different elements. Furthermore, the functionalities ofeach element may be distributed differently among the elements in otherembodiments.

The network 150, which can be wired, wireless, or a combination thereof,enables communications among the client devices 160, the DNS systems130/140, domain owner system 110, and third party system 120, and mayinclude the Internet, a LAN, VLAN (e.g., with VPN), WAN, or othernetwork. In one embodiment, the network 150 uses standard communicationstechnologies and/or protocols, such as Hypertext transfer Protocol(HTTP), Transmission Control Protocol/Internet Protocol (TCP/IP),Uniform Resource Locators (URLs), and the Doman Name System (DNS). Inanother embodiment, the entities can use custom and/or dedicated datacommunications technologies instead of, or in addition to, the onesdescribed above.

The domain owner system 110 includes one more computing systems of aparticular domain (e.g., examplecorp.com), which may be configuredsimilarly to the computing system described with reference to FIG. 4.

In one embodiment, the domain owner system 110 includes a rule creator111 that generates validation rules to allow receiving email systems,such as receiving email system 120, to verify the authenticity of emailsthat indicate the domain of the domain owner system 110 as the sender ofthe email. When a receiving email system 120 receives such an email, itmay check these validation rules to see if the email was in factlegitimately sent from the domain owner system 110. In one embodiment,the rule indicates an Internet Protocol (IP) address of the domain ownersystem 110, such that the receiving email system 120 verifies whetherthe email was received from the IP address indicated in the rule.

These rules may be automatically generated based on the detected networkcharacteristics (e.g., detected IP address of the sending email system,domain name information) or may be received by the rule creator 111 froman administrator through a user interface. Once the rules are generated,the rule creator 111 publishes the rules in a publicly accessiblelocation. This publicly accessible location is a trusted location whereonly the domain owner for the domain of the domain owner system 110 canpublish. Any receiving email system 120 may then access this publiclocation to retrieve the rules. In one embodiment, the public locationis the Domain Name System (DNS). Thus, these rules may be stored in anemail domain verification record 141 on domain owner DNS server 140. Inone embodiment, the rules are Sender Policy Framework (SPF) rules (whichare documented in RFC 4408 and 7208 and incorporated by referenceherein).

The delivering email system 115 sends email on behalf of the domainowner system 110. The delivering email system 115 comprises one or morecomputing systems, which may be configured similarly to the computingsystem described with reference to FIG. 4. As an example, the deliveringemail system 115 may be a mailing list server, a bulk mailer providerthat sends emails on behalf of a domain, a transactional email systemmanaged by a third party that sends emails on behalf of a domain, or asecurity system that scans emails on behalf of a domain. The deliveringemail system 115 may send the email instead of the domain owner system110 so that the delivering email system 115 may provide additionalprocessing or functionality to the email.

The delivering email system 115 includes an email sender 116 to sendemails. In one embodiment, the email sender 116 uses standard mailprotocols, such as Simple Mail Transfer Protocol (SMTP). SMTP supportsvarious features. In particular, when a sending email systemcommunicates with a receiving email system, SMTP indicates that thesending email system may send a HELO or extended HELO (EHLO) message tothe receiving email system. This HELO/EHLO message includes anidentifier of the sending email system (e.g., a domain name), and in thecase of an EHLO message, may include additional identifiers indicatingthe supported extensions and features of the sending email system.

When forwarding or otherwise transferring messages or emails that wereoriginally sent by the domain owner system 110, the validation rulesassociated with the domain owner system 110 and which may be stored asan email domain validation record 141 are modified such that they mayaccommodate the authentication of the delivering email system 115.

The receiving email system 120 is an email system that receives one ormore emails from the delivering email system 115. The receiving emailsystem 120 comprises one or more computing systems, which may beconfigured similarly to the computing system described with reference toFIG. 4.

The receiving email system 120 includes an email receiver 122 to receiveemails. In one embodiment, the email receiver 122 uses standard mailprotocols, such as Simple Mail Transfer Protocol (SMTP).

The receiving email system 120 comprises an email authenticator 121 tovalidate the identity of the sender of any received emails to ensurethat the email is not fraudulent. Upon receiving an email, the emailauthenticator 121 may look up any associated email domain validationrecord associated with either the identification provided by the serverfrom which the email was received (e.g., via a HELO command), or thedomain indicated in the Return-Path address of the email (e.g.,“gmail.com”), or via some other identifier. The email authenticator 121determines whether the information identified from the email, such asthe sender's IP address, matches or is allowed by any of the rulesindicated in any one of the associated email domain validation records.If a match is found in the rules, then the email authenticator 121determines that the email message is likely to be valid and is from thepurported sender and not from a fraudulent source.

In one embodiment, the rules indicated in the email domain validationrecords are SPF rules. An SPF rule may indicate an IP addresses, suchthat the email authenticator 121 may verify whether the IP addressindicated in the SPF rule matches the IP address or other identifyinginformation of the server that sent the email to the receiving emailsystem 120. An SPF rule may also indicate another domain, in which casethe email authenticator 121 may look up the SPF rule record for thatother domain to see if any rules in that record match the identifyinginformation of the server that sent the email. Additionally, in somecases, SPF rules support macros, which are special placeholderindicators that the email authenticator 121 substitutes with data thatis determined dynamically at the time of receipt of the email. Forexample, the email authenticator 121 may expand a macro such as “%{d}”which is indicated in the rule to the Return-Path domain of the email(e.g., “acme.com”). Additional macro commands are described in furtherdetail in the SPF RFCs 7208 and 4408.

The DNS servers 130 and 140 store DNS records for use in a DNS system.Each DNS server may comprise one or more computing systems such as thecomputing system described with reference to FIG. 4.

Each DNS server may store multiple DNS records for a particular domain,such an A record, MX record, and so on, as known in the art. Althoughthe records as illustrated in FIG. 1 are separated into multiple entriesand are on multiple servers, in other embodiments the records arecombined into fewer entries, a single server, a single entry, or someother combination. Furthermore, although a certain number of records foreach domain are illustrated in FIG. 1, in other embodiments each domainmay have multiple records.

As illustrated in FIG. 1, domain owner DNS server 140 includes an emaildomain validation record 141. This email domain validation record 141may include one or more rules that allow a receiving email system 120 tovalidate the authenticity of an email that it has received. As describedabove, the email domain validation record 141 may indicate an IP addressor other identifier for the sender associated with a domain, such thatthe receiving email system 120 may be able to verify that the IP address(or other identifier) of the sender of the email corresponds to thedomain indicated in the email (e.g., an email from “acmebank.com” isactually from Acme Bank). However, such a simple rule may bedisadvantageous in the case where a third party delivering email system115 is used to send mail on behalf of a sending email system or domainowner. This is because the rule in the email domain validation record141 may not indicate that the delivering email system 115 is a validsender for a particular domain.

Instead, the email domain validation record 141 may include a rule witha separate domain. The DNS records for this separate domain may existelsewhere, such as on authorizing DNS server 130. Furthermore, this rulewith the separate domain also includes one or more macros, that whenparsed by the receiving email system 120, cause the receiving emailsystem 120 to substitute the macros with additional informationidentifying the server from which the receiving email system 120received the email, or other identifying information regarding theemail. In one embodiment, this information includes any identifiers inan EHLO message from the server from which the receiving email system120 received the email, as well as the IP address of the same server.Once the rule is parsed, the receiving email system 120 is caused by therule to query the DNS records of the separate domain indicated in therule. For example, the rule may indicate a domain with macro of“%{i}._ip.verifier.com”. After expansion, the macro “%{i}” may bereplaced by the IP address of the server that sent the email to thereceiving email system 120 (e.g., this could be the delivering emailsystem 115), and the receiving email system 120 queries for the DNSrecords of the domain “verifier.com,” and passes the IP address to theDNS server that may provide the DNS record in question.

The DNS records for this separate domain may reside at (or may bequeried at) authorizing DNS server 130. The authorizing DNS server 130includes a deliverer/IP store 131 that stores information regardingdelivering email systems and their associated IP addresses and EHLOinformation. The authorizing DNS server 130 also includes adeliverer/record store that stores rules authenticating variousdelivering email systems. The authorizing DNS server 130 also includesan authorized deliverers list 132 that indicates the authorizeddelivering email systems for various domains.

The domain information, with the macros replaced by the identifyinginformation of the server that sent the email as described above, isreceived by the authorizing DNS server 130 from the receiving emailsystem 120 in a DNS query. The authorizing DNS server 130 includes anauthorization evaluator 135 that determines whether the server indicatedin the identifying information is authorized to send emails on behalf ofthe domain that is indicated in the identifying information. In oneembodiment, the domain is indicated from the EHLO information that ispassed to the authorizing DNS server 130 (via the use of the macro), andthe identifying information for the server is passed via an IP address.The authorization evaluator 135 accesses the deliverer/IP store 131 todetermine the identity of the delivering email system 115 associatedwith the identifying information. If such information is found, theauthorization evaluator accesses the authorized deliverers list 132 todetermine whether that delivering email system is an authorized deliveryagent for the domain indicated in the identifying information of the DNSquery.

If so, the authorizing DNS server 130 includes a target recordconstructor 133 that constructs a set of rules using thedeliverer/record store 134 as a response (to transmit) to the receivingemail system 130. This set of constructed rules indicates that thedelivering email system (e.g., the delivering email system 115) thatsent the email is a valid sender for the domain indicated in the email.The receiving email system 120 may then use the information in theresponse to verify that the delivering email system is a valid sender,and allow this email to be received by its intended recipient.Otherwise, if the delivering email system was indicated not to be validaccording to the response, then the receiving email system 120 mayinstead discard the email or flag it.

The client device 160 may be used to view emails that are received anauthenticated by the receiving email system 120. The client device 160may comprise a computing system such as the computing system describedwith reference to FIG. 4.

Specifically, the client device 160 includes an email client 165 tointerface with the receiving email system 120. The email client 165 mayuse standard email protocols, such as Post Office Protocol 3 (POP3),Internet Message Access Protocol (IMAP), Messaging ApplicationProgramming Interface (MAPI), SMTP, and so on, in order to communicatewith the receiving email system 120. In one embodiment, if an email isnot properly authenticated by the receiving email system 120, the emailclient 165 does not receive the email. In other embodiments, the emailclient 165 may receive the email but also receive an indication that theemail is suspected to be fraudulent or suspicious.

Using the system 100 described above, a domain owner is able to utilizethe services of other third party delivering organizations and theirdelivering email systems in order to send emails and still have theseemails be validated by receiving email systems 120 as being authentic.Instead of updating a variety of email domain validation records, a DNSserver may, in a centralized location, construct a simple set of rulesdepending on the identifying information received from a receiving emailsystem 120 for the delivering email system 115 which sent the email.Furthermore, the receiving email system 120 does not need to query alarge number of DNS records that may be present in rules in an emaildomain validation record. This increases performance and simplifies themanagement of sending emails via third party agents, while stillproviding security and preventing fraudulent or suspicious messages frombeing received. Additional details regarding the systems and processesdescribed above are described with reference to FIGS. 2-3.

Example Interaction Diagram for Email Domain Validation Record Creation

FIG. 2 is an interaction diagram and flow chart illustrating anexemplary process for creation of an email domain validation record foruse with a third party delivering organization according to oneembodiment. In one embodiment, FIG. 2 attributes the operations inprocess to the indicated elements. However, some or all of the steps maybe performed by other elements. In addition, some embodiments mayperform the operations in parallel, perform the operations in differentorders, or perform different operations. Also, it is noted that in oneexample embodiment the steps and/or modules may be embodied asinstructions, e.g., instructions 424, that may be executed by theprocessor 402 described with respect to FIG. 4.

For the purposes of this discussion, an email domain shall refer to anydomain that a receiving email system 120 may use as the ‘domain’ whenevaluating SPF for an inbound email message. Typically, this will be thedomain found in the Return-Path for the message.

The domain owner system 110, which is the email domain owner, or adesignated party, may configure the DNS record for the email domain.This may involve creating (or generating) 210 an email domain validationrecord 141 (which may be an SPF record) for use with the email domain.The record indicates that a particular sender is a valid sender for anemail from the email domain. In one embodiment, the record is an SPFrecord and is constructed so that it may incorporate a specific“include” directive. The include directive may indicate a targeted SPFdomain specification, which indicates another domain, such that some orall of the SPF authentication decision for a message is deferred to theSPF record found at the other domain. In other words, as describedabove, the record includes a separate domain which is separately queriedto determine the final SPF authentication information.

In one embodiment, the targeted SPF domain specification in the emaildomain validation record 141 may be configured to dynamically changebehavior for an email message based on the SMTP connection attributesfor that message. This change may be accomplished by causing thereceiving server to use the SMTP connection attributes and email domainto build a custom domain name which, when resolved, yields a targetedSPF record that applies to the message being processed.

To accomplish this, in one embodiment, the targeted SPF domainspecification may comprise three properties. First, it may beconstructed such that the eventual authority for any domain nameresolved from the targeted SPF domain specification is a targeted DNSSPF resolver (e.g., authorizing DNS server 130).

This may be accomplished by ensuring that the targeted domainspecification eventually resolves to a subdomain of one or moreparticular fixed domains. In some implementations the DNS recordcontaining the targeted SPF domain specification may be hidden behindone or more DNS CNAME or NS records referring to other domains, and notmanaged by the targeted DNS SPF resolver. This allows for redirection ormasking of the eventual DNS query target. In other words, the otherdomains may need to be queried by a receiving email system before thefinal DNS query target is determined.

Second, the targeted SPF domain specification may cause a receivingemail system 120 to capture the EHLO name and/or the IP address for theSMTP connection. These values may be captured using the SPF macrosystem. The %{h} macro can be used to capture the EHLO name, and the%{i} or %{p} macros can be used to the capture the IP address or thevalidated domain name of the IP address. In some embodiments, the domainowner system 110 may configure the targeted SPF domain specification toalso cause the receiving email system 120 to capture the local part ofthe sender address or the complete sender address with either the %{l}and/or %{s} macros, and encode the resulting values into the targetedSPF domain specification.

Depending on the exact configuration of the system, one or more of theoptional transformers described in the SPF macro language may be appliedin the targeted SPF domain specification. Similarly, the uppercasevariants %{H}, %{I}, %{P}, %{L}, or %{S} may be used instead, so thatthe result is URL encoded.

Third, the targeted SPF domain specification may be constructed in sucha way that the SMTP connection attributes can be parsed unambiguouslyfrom the resulting domain, which can actually be accomplished for realworld systems.

To demonstrate this, a format for the targeted SPF domain specificationthat meets these three requirements may be constructed. For example,assume that the targeted DNS SPF resolver (e.g. authorizing DNS server130) responds to all DNS TXT queries in the zone defined by the domain‘resolver.com’. Also assume that the email domain is ‘emaildomain.com’.Finally, assume that both the EHLO name and the IP address are captured.

In this case the Letters-Digits-Hyphen (LDH) rules for hostnames may beused. These rules include the restriction that fully qualified domainnames (FQDN) can only contain ASCII letters, numbers, or the hyphencharacter. More generally domains, including those used in SPF recordlookups, do not need to meet this restriction. As both the EHLO name andthe email domain are required to be FQDNs, these fields may be separatedby the domain owner system 110 when creating the targeted SPF domainspecification with labels that contain non-LDH characters such as ‘_’.Since an IP address can only consist of digits (IPv4) or digits and theletters a-f (IPv6), the labels comprising the IP address cannot contain‘_’ either. Thus, labels containing ‘_’ may be used as separators forthese values as well.

Combining all of the above, one targeted SPF domain specification thatmeets the requirements within the context of the example is:‘{i}._ipaddr.%{h}._ehlo.emaildomain.com._tspf.resolver.com’. Any domainname interpolated during the SPF process from this domain spec will berooted in ‘resolver.com’ (the rightmost domain indicated). It includesboth the EHLO name and IP address in the domain name. Furthermore, theuse of labels containing ‘_’ supports non-ambiguous parsing of the SMTPattributes from such a domain name.

Note that there are a large number of potential formats that meet theserequirements, and this particular example should be considerednon-limiting.

The email domain validation record 141 should then have an SPF rule thathas an include directive that refers to a targeted SPF domainspecification as described above. A simple, non-limiting example of sucha record that uses the example targeted SPF domain specificationdescribed above would be ‘v=spf1include:%{i}._ipaddr.%{h}._ehlo.emaildomain.com._tspf.resolver.com’.Again, while this record is realistic for our example, it should beconsidered non-limiting. Note that “v” refers to the SPF version, andthe include directive indicates that the domain indicated is a validsender for the email domain.

Once the email domain validation record 141 is constructed, it may bepublished 215 as a DNS TXT record for the email domain (e.g., at domainowner DNS server 140). This will allow it to be queried by any serverthat receives email that indicates this domain.

Example Interaction Diagram for Email Verification Rule Resolution

FIG. 3 is an interaction diagram and flow chart illustrating anexemplary process for resolution of an email domain validation recordusing DNS according to one embodiment. In one embodiment, FIG. 3attributes the operations in process to the indicated elements. However,some or all of the steps may be performed by other elements. Inaddition, some embodiments may perform the operations in parallel,perform the operations in different orders, or perform differentoperations. Also, it is noted that in one example embodiment the stepsand/or modules may be embodied as instructions, e.g., instructions 424,that may be executed by the processor 402 described with respect to FIG.4. Note that the processes described here do not necessarily require anyadditional modification or configuration of the receiving email system120. Instead, so long as the receiving email system 120 supports SPF ora similar sender authentication scheme, it does not need to be modified.

Initially, the receiving email system 120 receives 310 an email with areturn path corresponding to a particular email domain. The receivingemail system 120 may attempt to authenticate this email message (e.g.,using SPF). The receiving email system 120 may first query 315 DNS forany email validation records for the email domain. These may be SPFrecords. The domain owner DNS server 140 may return the email domainvalidation record 141 in a response 282 that the owner of the emaildomain has published as described with reference to FIG. 2.

The receiving email system 120 parses the email validation record, andgenerates 320 a target domain query. This process may include evaluatingthe include directive with the target domain SPF specification in thereturned DNS record using values for the current SMTP connection (e.g.,EHLO, IP address), and interpolating these values into the target domainSPF specification to construct the target domain. For example, if therecord indicates a rule of‘%{i}._ipaddr.%{h}._ehlo.emaildomain.com._tspf.resolver.com’, thereceiving email system 120 may evaluate this into“‘123.123.123.123._ipaddr.deliveringdomain.com._ehlo.emaildomain.com._tspf.resolver.com’assuming that 123.123.123.123 is the IP address of the sender,emaildomain.com is the domain of the original sender, anddeliveringdomain.com is the domain name indicated in the EHLO messagefor the sender.

The receiving email system 120 then queries 325 the DNS with the targetdomain. This query may be responded to by the authorizing DNS server 130(which may be an authoritative server for the target domain). Theauthorizing DNS server 130 extracts 340 the identifying information fromthe query. This identifying information may include the EHLO name and IPaddress, and may be parsed from the target domain query. In oneembodiment, the authorizing DNS server 130 may also parse the local partof the Return-Path address from target domain of the query, either as astand-alone value or as part of an encoded complete sender address.

In one embodiment, the authorizing DNS server 130 also extracts theemail domain from the target domain query (if it has been included inthe query via a macro). If the email domain is present and, if theauthorizing DNS server 130 is configured to only process requests for alimited set of domains, then the domain owner DNS server 130 candetermine if the email domain is known. In this case the authorizing DNSserver 130 may return a default SPF record if the email domain is notknown. The returned record is likely to be a record that does not passany IP address—an example would be “v=spf1˜all”.

The authorizing DNS server 130 uses the identifying information that isextracted from the query to identify 345 the delivering organization.The delivering organization is the owner of the delivering email system115, which may not be part of the email domain. The authorizing DNSserver 130 includes a deliverer/IP store 131 that associates theidentifying information extracted from the query with deliveringorganizations such that network specific information associated with anemail message's SMTP connection (e.g., EHLO name and/or sending serverIP address) may be associated with the higher-level abstraction of adelivering organization.

Some examples of common delivering organizations are third party senderscontracted to send email by the email domain owner, a mailing list thatis relaying a message originating from the email domain to a number ofreceiving addresses, or a forwarding system that is designed to aliasone receiver address to another. This set of examples should not beconsidered exhaustive, and the list should be considered non-limiting.

In one embodiment, access to the header information of a substantial(i.e., statistically significant) corpus of email (100s of millions ofmessages or more) may allow the authorizing DNS server 130 or otherentity to construct the deliverer/IP store 131 by use of informationfound in the email headers (specifically the ‘Received’ and‘Authentication-Results’ headers). In other embodiments, one couldsurvey a list of delivering organizations, and combine the results intoa suitable deliverer/IP store 131. In further embodiments, domainregistration records, especially the information stored in the WHOISdatabase, can be useful for building this mapping for the deliverer/IPstore 131. These example methods should be considered non-limiting, andthe process described herein does not preclude the use of other methodsor the combination of multiple methods for the construction of thedeliverer/IP store 131.

In further embodiments, the inbound stream of DNS queries received bythe authorizing DNS server 130 can be used as a source of EHLO names andIP addresses that require investigation. For a complete database all(EHLO Name, IP Address) combinations originating from legitimate emailshould map to a known delivering organization. Any inbound data thatcannot be mapped to a known delivering organization may generallyindicate a) missing legitimate values in the database or b) a sourceemail that is fraudulent. This ‘miss’ can thus serve as a source ofinformation to fill in gaps in the database or a source of threatinformation.

Once the request has been mapped to a delivering organization, in oneembodiment the authorizing DNS server 130 may determine 348 if thedelivering organization is a known one. If not, then a default recordmay be returned, such as some variation on an SPF record that fails allIP addresses. For example, ‘v=spf1˜all’, would be a likely choice.

Assuming that the delivering organization is known, then the authorizingDNS server 130 can determine 350 whether the delivering organization isauthorized to deliver email for the email domain indicated in the queryfor the target domain. In one embodiment, the authorizing DNS server 130allows any identified delivering organization to deliver email for anyemail domain. In another embodiment, the mapping of email domain toauthorized delivering organization could be stored in an authorizeddeliverers list 132, or made available via a web API, and theauthorizing DNS server 130 accesses the list or API to determine whetherthe delivering organization is authorized.

If the identified delivering organization is not found to be authorizedfor the email domain, then the authorizing DNS server 130 may return adefault record. In general this may be a record denying delivery for allIP addresses (e.g. ‘v=spf1˜all’).

As described above, in one embodiment, the local part of the Return-Pathaddress may have been encoded in the query of the target domain eitheras a standalone value, or as part of the sender address. In theseembodiments, the authorizing DNS server 130 uses the local part of theemail address in combination with the email domain to determine whethera delivering organization is authorized to deliver a particular message.For example, a delivering organization may be authorized to send mail onbehalf of a “newsletter@acme.com” but not on behalf of a return pathaddress with a local part indicating an email address of an employee atacme.com.

If the delivering organization is authorized to deliver email for theemail domain, then the authorizing DNS server 130 generates 355 a targetvalidation record (which may be an SPF record) based on the deliveringorganization and the email domain. To construct this record, theauthorizing DNS server 130 may query a deliverer/record store 134 thatincludes a map of delivering organizations to target validation records.

For each delivering organization, there may exist some hypotheticalemail validation record that would allow email from servers used by thatdelivering organization (e.g., the delivering email system 115), anddeny email originating anywhere else. This should be true for anydelivering organization that has a properly configured email domainvalidation record (e.g., an SPF record), as the existing email domainvalidation record for the delivering organization may be used.

Even if a delivering organization does not have a properly configuredemail domain validation record, the authorizing DNS server 130 oradministrator may be able to build such a record given sufficientknowledge of the underlying network configuration. In one embodiment,the authorizing DNS server 130 creates and stores the email domainvalidation records for delivering organizations and/or email domainsthat are not otherwise made available by the delivering organization.

In some embodiments, and for some configurations, the deliverer/recordstore 134 also associates the email domain and/or the local path aseither a replacement or a supplement to the association of thedelivering organization with the target validation record. As an exampleof when such a variation may be desirable, consider a deliveringorganization that subdivides its cloud of mail servers by email domain.In such circumstances it may be necessary to know the email domain, incombination with the delivering organization, to deliver the optimaltarget validation record.

In some embodiments, existing email domain validation records may be animportant source of information to construct the deliverer/record store134. For example, in the case of SPF records, the existing records forthe delivering organization may be used to get a list of directives. Inother embodiments, a manual survey of the delivering organizations canalso be a good source of this information. In further embodiments,additional methods may also be feasible, as is the use of combinationsof sources. The sources listed here should be considered non-limiting.

When using these or any other methods to construct the deliverer/recordstore 134, it may be necessary to update the data as the underlyingnetwork configuration changes with time. In some embodiments, theauthorizing DNS server 130 may use polling mechanisms to update thedeliverer/record store 134, while in other embodiments. A non-limitingexample of such a polling mechanism would be a software component on theauthorizing DNS server 130 that executes DNS queries on a regular (e.g.daily) basis to detect updates to DNS records published by knownsenders. Those updates could then be incorporated by the authorizing DNSserver 130 into the database.

After generating the target validation record, the authorizing DNSserver 130 transmits 360 the record back to the receiving mail system120 as a response to the original query.

The receiving mail system 120 authenticates 330 the email message usingthe received target validation record.

In one embodiment, instead of instead of using the ‘include’ mechanismof SPF as described above, the system described here may be configuredto use the ‘a’, ‘mx’, or ‘exists’ mechanisms that are part of SPF. Ifone of these mechanisms is used, the behavior of the email domain ownermay be largely unchanged—the ‘a’, ‘mx’, or ‘exists’ mechanism may besimply substituted for the ‘include’ mechanism in this case.

Under this variation the behavior of the authorizing DNS server 130 ismostly unchanged, except for its return values. In the cases where theauthorizing DNS server 130 indicates that the message is notauthenticated, the authorizing DNS server 130 may return an NXDOMAINcode. And instead of returning a target validation record, theauthorizing DNS server 130 may match the IP address against the targetvalidation record. If the IP address does not match the record, then theauthorizing DNS server 130 may return an NXDOMAIN. Alternately, if theIP address is found to match, then the authorizing DNS server 130 mayreturn an A, MX, or A record that includes the IP address.

In one embodiment, the authorizing DNS server 130 is used as a remoteSPF auditing tool. SPF resolution occurs on the receiving email system120, and as such the results of that evaluation may not generally beavailable to external auditing systems unless special software isinstalled. If the targeted SPF domain specification has been structuredto include both the EHLO name and IP address, the authorizing DNS server130 may be invoked at least once for each (EHLO name, IP address)combination from which a message is delivered. With this information theresolver can mirror the SPF evaluation carried out by the receivingemail system 120 and log the corresponding result.

Example Machine Architecture

FIG. 4 is a block diagram illustrating components of an example machineable to read instructions from a machine-readable medium and executethem in a processor (or controller). Specifically, FIG. 4 shows adiagrammatic representation of a machine in the example form of acomputer system 400. The computer system 400 can be used to executeinstructions 424 (e.g., program code or software) for causing themachine to perform any one or more of the methodologies (or processes)described herein. In alternative embodiments, the machine operates as astandalone device or a connected (e.g., networked) device that connectsto other machines. In a networked deployment, the machine may operate inthe capacity of a server machine or a client machine in a server-clientnetwork environment, or as a peer machine in a peer-to-peer (ordistributed) network environment.

The machine may be a server computer, a client computer, a personalcomputer (PC), a tablet PC, a set-top box (STB), a smartphone, aninternet of things (IoT) appliance, a network router, switch or bridge,or any machine capable of executing instructions 424 (sequential orotherwise) that specify actions to be taken by that machine. Further,while only a single machine is illustrated, the term “machine” shallalso be taken to include any collection of machines that individually orjointly execute instructions 424 to perform any one or more of themethodologies discussed herein.

The example computer system 400 includes one or more processing units(generally processor 402). The processor 402 is, for example, a centralprocessing unit (CPU), a graphics processing unit (GPU), a digitalsignal processor (DSP), a controller, a state machine, one or moreapplication specific integrated circuits (ASICs), one or moreradio-frequency integrated circuits (RFICs), or any combination ofthese. The computer system 400 also includes a main memory 404. Thecomputer system may include a storage unit 416. The processor 402,memory 404 and the storage unit 416 communicate via a bus 408.

In addition, the computer system 406 can include a static memory 406, adisplay driver 410 (e.g., to drive a plasma display panel (PDP), aliquid crystal display (LCD), or a projector). The computer system 400may also include alphanumeric input device 412 (e.g., a keyboard), acursor control device 414 (e.g., a mouse, a trackball, a joystick, amotion sensor, or other pointing instrument), a signal generation device418 (e.g., a speaker), and a network interface device 420, which alsoare configured to communicate via the bus 408.

The storage unit 416 includes a machine-readable medium 422 on which isstored instructions 424 (e.g., software) embodying any one or more ofthe methodologies or functions described herein. The instructions 424may also reside, completely or at least partially, within the mainmemory 404 or within the processor 402 (e.g., within a processor's cachememory) during execution thereof by the computer system 400, the mainmemory 404 and the processor 402 also constituting machine-readablemedia. The instructions 424 may be transmitted or received over anetwork 426 via the network interface device 420.

While machine-readable medium 422 is shown in an example embodiment tobe a single medium, the term “machine-readable medium” should be takento include a single medium or multiple media (e.g., a centralized ordistributed database, or associated caches and servers) able to storethe instructions 424. The term “machine-readable medium” shall also betaken to include any medium that is capable of storing instructions 424for execution by the machine and that cause the machine to perform anyone or more of the methodologies disclosed herein. The term“machine-readable medium” includes, but not be limited to, datarepositories in the form of solid-state memories, optical media, andmagnetic media.

Additional Considerations

Using the system and processes described above, a domain owner is ableto utilize the services of other third party delivering organizationsand their delivering email systems in order to send emails and stillhave these emails be validated by receiving email systems as beingauthentic. Instead of updating a variety of email domain validationrecords, a DNS server may, in a centralized location, generate a simpleset of rules depending on the identifying information received from areceiving email system for the delivering email system which sent theemail. Furthermore, the receiving email system does not need to query alarge number of DNS records that may be present in rules in an emaildomain validation record. This increases performance and simplifies themanagement of sending emails via third party agents, while stillproviding security and preventing fraudulent or suspicious messages frombeing received.

Throughout this specification, plural instances may implementcomponents, operations, or structures described as a single instance.Although individual operations of one or more methods are illustratedand described as separate operations, one or more of the individualoperations may be performed concurrently, and nothing requires that theoperations be performed in the order illustrated. Structures andfunctionality presented as separate components in example configurationsmay be implemented as a combined structure or component. Similarly,structures and functionality presented as a single component may beimplemented as separate components. These and other variations,modifications, additions, and improvements fall within the scope of thesubject matter herein.

Certain embodiments are described herein as including logic or a numberof components, modules, or mechanisms, for example, as illustrated inFIGS. 1-5. Modules may constitute either software modules (e.g., codeembodied on a machine-readable medium or in a transmission signal) orhardware modules. A hardware module is tangible unit capable ofperforming certain operations and may be configured or arranged in acertain manner. In example embodiments, one or more computer systems(e.g., a standalone, client or server computer system) or one or morehardware modules of a computer system (e.g., a processor or a group ofprocessors) may be configured by software (e.g., an application orapplication portion) as a hardware module that operates to performcertain operations as described herein.

In various embodiments, a hardware module may be implementedmechanically or electronically. For example, a hardware module maycomprise dedicated circuitry or logic that is permanently configured(e.g., as a special-purpose processor, such as a field programmable gatearray (FPGA) or an application-specific integrated circuit (ASIC)) toperform certain operations. A hardware module may also compriseprogrammable logic or circuitry (e.g., as encompassed within ageneral-purpose processor or other programmable processor) that istemporarily configured by software to perform certain operations. Itwill be appreciated that the decision to implement a hardware modulemechanically, in dedicated and permanently configured circuitry, or intemporarily configured circuitry (e.g., configured by software) may bedriven by cost and time considerations.

The various operations of example methods described herein may beperformed, at least partially, by one or more processors that aretemporarily configured (e.g., by software) or permanently configured toperform the relevant operations. Whether temporarily or permanentlyconfigured, such processors may constitute processor-implemented modulesthat operate to perform one or more operations or functions. The modulesreferred to herein may, in some example embodiments, compriseprocessor-implemented modules.

The one or more processors may also operate to support performance ofthe relevant operations in a “cloud computing” environment or as a“software as a service” (SaaS). For example, at least some of theoperations may be performed by a group of computers (as examples ofmachines including processors), these operations being accessible via anetwork (e.g., the Internet) and via one or more appropriate interfaces(e.g., application program interfaces (APIs).)

The performance of certain of the operations may be distributed amongthe one or more processors, not only residing within a single machine,but deployed across a number of machines. In some example embodiments,the one or more processors or processor-implemented modules may belocated in a single geographic location (e.g., within a homeenvironment, an office environment, or a server farm). In other exampleembodiments, the one or more processors or processor-implemented modulesmay be distributed across a number of geographic locations.

Some portions of this specification are presented in terms of algorithmsor symbolic representations of operations on data stored as bits orbinary digital signals within a machine memory (e.g., a computermemory). These algorithms or symbolic representations are examples oftechniques used by those of ordinary skill in the data processing artsto convey the substance of their work to others skilled in the art. Asused herein, an “algorithm” is a self-consistent sequence of operationsor similar processing leading to a desired result. In this context,algorithms and operations involve physical manipulation of physicalquantities. Typically, but not necessarily, such quantities may take theform of electrical, magnetic, or optical signals capable of beingstored, accessed, transferred, combined, compared, or otherwisemanipulated by a machine. It is convenient at times, principally forreasons of common usage, to refer to such signals using words such as“data,” “content,” “bits,” “values,” “elements,” “symbols,”“characters,” “terms,” “numbers,” “numerals,” or the like. These words,however, are merely convenient labels and are to be associated withappropriate physical quantities.

Unless specifically stated otherwise, discussions herein using wordssuch as “processing,” “computing,” “calculating,” “determining,”“presenting,” “displaying,” or the like may refer to actions orprocesses of a machine (e.g., a computer) that manipulates or transformsdata represented as physical (e.g., electronic, magnetic, or optical)quantities within one or more memories (e.g., volatile memory,non-volatile memory, or a combination thereof), registers, or othermachine components that receive, store, transmit, or displayinformation.

As used herein any reference to “one embodiment” or “an embodiment”means that a particular element, feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment.

Some embodiments may be described using the expression “coupled” and“connected” along with their derivatives. For example, some embodimentsmay be described using the term “coupled” to indicate that two or moreelements are in direct physical or electrical contact. The term“coupled,” however, may also mean that two or more elements are not indirect contact with each other, but yet still co-operate or interactwith each other. The embodiments are not limited in this context.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive or and not to an exclusive or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

In addition, use of the “a” or “an” are employed to describe elementsand components of the embodiments herein. This is done merely forconvenience and to give a general sense of the invention. Thisdescription should be read to include one or at least one and thesingular also includes the plural unless it is obvious that it is meantotherwise.

Upon reading this disclosure, those of skill in the art will appreciatestill additional alternative structural and functional designs for asystem and a process capable of validating email senders throughintermediaries via EHLO name and IP address targeting. Thus, whileparticular embodiments and applications have been illustrated anddescribed, it is to be understood that the disclosed embodiments are notlimited to the precise construction and components disclosed herein.Various modifications, changes and variations, which will be apparent tothose skilled in the art, may be made in the arrangement, operation anddetails of the method and apparatus disclosed herein without departingfrom the spirit and scope defined in the appended claims.

What is claimed is:
 1. A system, comprising: an interface configured toreceive one or more inputs for indicating that one or more deliveringorganizations are organizations that deliver emails on behalf of adomain owner that owns an email domain, wherein a particular deliveringorganization of the one or more delivering organizations delivers emailsvia one or more IP addresses; and a domain name system (DNS) servercomprising memory and one or more processors, the DNS server configuredto provide one or more DNS responses on behalf of the domain owner,wherein the DNS server, the domain owner, and the particular deliveringorganization are different entities, wherein the memory comprisesinstructions that when executed by the one or more processors cause theone or more processors to: store a deliverer list associated with thedomain owner, the deliverer list comprising one or more deliveringorganizations; maintain a mapping between the particular deliveringorganization and the one or more IP addresses used by the particulardelivering organization; serve as an authoritative DNS server for atarget domain, wherein the target domain is different from the emaildomain, the target domain being connected with the email domain throughone or more DNS lookup statements; receive, from a receiving emailsystem attempting to authenticate an incoming email, a DNS query to thetarget domain, wherein the DNS query to the target domain is generatedafter the receiving email system first queried the email domain; andreturn, responsive to the DNS query, a DNS record that comprises atleast one of the IP addresses used by the particular deliveringorganization to deliver emails, wherein the DNS record leads to thereceiving email system determining whether to authenticate the incomingemail.
 2. The system of claim 1, wherein the target domain has a namethat includes both the email domain and a domain of an entity associatedwith the DNS server as part of the name.
 3. The system of claim 1,wherein the target domain is referenced in DNS information associatedwith the email domain via an include directive, the include directivecomprising a statement that includes the email domain and a domain of anentity associated with the DNS server.
 4. The system of claim 1, whereinthe target domain is a subdomain of a domain of an entity associatedwith the DNS server, and the subdomain has the email domain as a prefixto the domain of the entity.
 5. The system of claim 1, wherein the DNSrecord leads to the receiving email system determining whether toauthenticate the incoming email by (i) including an IP address list thatincludes the one or more IP addresses used by the particular deliveringorganization to allow the receiving email system to compare a sender IPaddress to the IP address list or (ii) including a directive that pointsto another DNS record.
 6. The system of claim 1, wherein the DNS recordis generated by retrieving the mapping between the particular deliveringorganization and the one or more IP addresses.
 7. The system of claim 1,wherein the deliverer list includes a plurality of deliveringorganizations, each delivering organization has one or more DNS recordsto list the delivering organization's own IP addresses, and wherein theplurality of delivering organizations, in total and without the DNSrecord of the target domain, have a total number of DNS recordsexceeding a lookup limit.
 8. The system of claim 1, wherein the DNSquery to the target domain is a second DNS query by the receiving emailsystem, and wherein the receiving email system, upon receiving theincoming email, generates a first DNS query directed to the email domainand, based on an include directive in a DNS response to the first DNSquery, the receiving email system generates the second DNS query.
 9. Thesystem of claim 1, wherein the interface is a graphical user interfaceand the interface and the DNS server are operated by the same entity.10. The system of claim 1, wherein the mapping is constructed by goingthrough existing Sender Policy Framework records of the particulardelivering organization to collect the one or more IP addresses used bythe particular delivering organization.
 11. A system comprising: one ormore processors; and memory configured to store code comprisinginstructions, wherein the instructions, when executed by the one or moreprocessors, cause the one or more processors to: receive one or moreinputs for indicating that one or more delivering organizations areorganizations that deliver emails on behalf of a domain owner that ownsan email domain, wherein a particular delivering organization of the oneor more delivering organizations delivers emails via one or more IPaddresses; store a deliverer list associated with the domain owner, thedeliverer list comprising one or more delivering organizations; maintaina mapping between the particular delivering organization and the one ormore IP addresses used by the particular delivering organization; causea domain name system (DNS) server to serve as an authoritative DNSserver for a target domain, wherein the target domain is different fromthe email domain, wherein the target domain is connected with the emaildomain through one or more DNS lookup statements, and wherein the DNSserver, the domain owner, and the particular delivering organization aredifferent entities; receive, from a receiving email system attempting toauthenticate an incoming email, a DNS query to the target domain,wherein the DNS query to the target domain is generated after thereceiving email system first queried the email domain; and return,responsive to the DNS query, a DNS record that comprises at least one ofthe IP addresses used by the particular delivering organization todeliver emails, wherein the DNS record leads to the receiving emailsystem determining whether to authenticate the incoming email.
 12. Thesystem of claim 11, wherein the target domain has a name that includesboth the email domain and a domain of an entity associated with the DNSserver as part of the name.
 13. The system of claim 11, wherein thetarget domain is referenced in DNS information associated with the emaildomain via an include directive, the include directive comprising astatement that includes the email domain and a domain of an entityassociated with the DNS server.
 14. The system of claim 11, wherein thetarget domain is a subdomain of a domain of an entity associated withthe DNS server, and the subdomain has the email domain as a prefix tothe domain of the entity.
 15. The system of claim 11, wherein the DNSrecord leads to the receiving email system determining whether toauthenticate the incoming email by (i) including an IP address list thatincludes the one or more IP addresses used by the particular deliveringorganization to allow the receiving email system to compare a sender IPaddress to the IP address list or (ii) including a directive that pointsto another DNS record.
 16. The system of claim 11, wherein the DNSrecord is generated by retrieving the mapping between the particulardelivering organization and the one or more IP addresses.
 17. The systemof claim 11, wherein the deliverer list includes a plurality ofdelivering organizations, each delivering organization has one or moreDNS records to list the delivering organization's own IP addresses, andwherein the plurality of delivering organizations, in total and withoutthe DNS record of the target domain, have a total number of DNS recordsexceeding a lookup limit.
 18. The system of claim 11, wherein the DNSquery to the target domain is a second DNS query by the receiving emailsystem, and wherein the receiving email system, upon receiving theincoming email, generates a first DNS query directed to the email domainand, based on an include directive in a DNS response to the first DNSquery, the receiving email system generates the second DNS query. 19.The system of claim 11, wherein the one or more inputs are received froma graphical user interface and the interface and the DNS server areoperated by the same entity.
 20. The system of claim 11, wherein themapping is constructed by going through existing Sender Policy Frameworkrecords of the particular delivering organization to collect the one ormore IP addresses used by the particular delivering organization.
 21. Acomputer-implemented method, comprising: receiving one or more inputsfor indicating that one or more delivering organizations areorganizations that deliver emails on behalf of a domain owner that ownsan email domain, wherein a particular delivering organization of the oneor more delivering organizations delivers emails via one or more IPaddresses; storing a deliverer list associated with the domain owner,the deliverer list comprising one or more delivering organizations;maintaining a mapping between the particular delivering organization andthe one or more IP addresses used by the particular deliveringorganization; causing a domain name system (DNS) server to serve as anauthoritative DNS server for a target domain, wherein the target domainis different from the email domain, wherein the target domain isconnected with the email domain through one or more DNS lookupstatements, and wherein the DNS server, the domain owner, and theparticular delivering organization are different entities; receiving,from a receiving email system attempting to authenticate an incomingemail, a DNS query to the target domain, wherein the DNS query to thetarget domain is generated after the receiving email system firstqueried the email domain; and returning, responsive to the DNS query, aDNS record that comprises at least one of the IP addresses used by theparticular delivering organization to deliver emails, wherein the DNSrecord leads to the receiving email system determining whether toauthenticate the incoming email.
 22. The computer-implemented method ofclaim 21, wherein the target domain has a name that includes both theemail domain and a domain of an entity associated with the DNS server aspart of the name.
 23. The computer-implemented method of claim 21,wherein the target domain is referenced in DNS information associatedwith the email domain via an include directive, the include directivecomprising a statement that includes the email domain and a domain of anentity associated with the DNS server.
 24. The computer-implementedmethod of claim 21, wherein the target domain is a subdomain of a domainof an entity associated with the DNS server, and the subdomain has theemail domain as a prefix to the domain of the entity.
 25. Thecomputer-implemented method of claim 21, wherein the DNS record leads tothe receiving email system determining whether to authenticate theincoming email by (i) including an IP address list that includes the oneor more IP addresses used by the particular delivering organization toallow the receiving email system to compare a sender IP address to theIP address list or (ii) including a directive that points to another DNSrecord.
 26. The computer-implemented method of claim 21, wherein the DNSrecord is generated by retrieving the mapping between the particulardelivering organization and the one or more IP addresses.
 27. Thecomputer-implemented method of claim 21, wherein the deliverer listincludes a plurality of delivering organizations, each deliveringorganization has one or more DNS records to list the deliveringorganization's own IP addresses, and wherein the plurality of deliveringorganizations, in total and without the DNS record of the target domain,have a total number of DNS records exceeding a lookup limit.
 28. Thecomputer-implemented method of claim 21, wherein the DNS query to thetarget domain is a second DNS query by the receiving email system, andwherein the receiving email system, upon receiving the incoming email,generates a first DNS query directed to the email domain and, based onan include directive in a DNS response to the first DNS query, thereceiving email system generates the second DNS query.
 29. Thecomputer-implemented method of claim 21, wherein the one or more inputsare received from a graphical user interface and the interface and theDNS server are operated by the same entity.
 30. The computer-implementedmethod of claim 21, wherein the mapping is constructed by going throughexisting Sender Policy Framework records of the particular deliveringorganization to collect the one or more IP addresses used by theparticular delivering organization.